High-frequency carrier signaling



Aug. 4; 1925,

R. A. HEISING.

HIGH FREQUENCY CARRIER SIGNALING. I

Filed March 26, 1920 w s w aw R inn in it 116.5131

RAYMOND A. HEISING, 01: EAST GRANGE, NEW' JERSEY, A'SSIGNQR T0 WESTERN ELECTRIC CUMFE'ANY, INGQEPORATED, 933 NEW YORK, N. Y., A COBIPORATION O1" NERV YORK.

HIGH-EELEQUENCY CAEMER SIGNALING.

, i Application filed March 26, 1920. Serial No. 388,881.

cants Patent No. 1313,4515 granted August it), ii lili means of a system of the type disclosed in the above-nientioued patent. it possible to transmit several messages simul-- tancously from one station by means of voice lllUlilllltttl carrier waves of high frequency and at the same time to receive simultaneously several messages, transmitted from another station in the sanie'nuinner, i. e, by means f voice. modulated iarricr waves of high frequency. Th present invention relates to a particular relationship between the frcruiencies of the outgoing and the incoming waves, i. between the waves sent over the line by one station and the waves sent over the line in the opposite direction by the distant station.

in the type multiplex telephmic system disclosed in the patent. a plurality of messages can be sinrultaneously sent over the line by means of the expedicniin which each one of a plurality of transmitters sends out a modulated were having a chaactcristic frequency, which frequency is ditfcrcnt from that of the other transmitters. 'lhe. receiving devices at the. distant end of the line are tuned to the respective frequencies of the corresponding transmitting circuits. A plurality of n'iessagcs can be transmitted over the line in the, opposite direction in the same manner. and the transmission and reception of signals in opposite directions can be carried on simultanemisl In an early system of this general type. the frequencies transniill'cd inthe two directions were the same, t the frequency range occupied by the a whole was the same as the fre- 1y range occupied by the frequencies at either of the stations was working.

By means of-this arrangement, a maximum economy of frequency range can be obtained. as is readily apparent. This arrangement, however; has been found to be ineflicient and incapable of commercial use on account of interference between transmitting and receiving circuits at the same station .and between receiving circuits at; either station. In order to avoid interference efiects, the frequency ranges for the frequencies transmitted in the two directions were then made to occupy adjacent but separate frequency ranges. By means of this arrangement, there was a minimum interference effect, but the frequency range of the system, by means of which the same number of messages could be transmitted simultaneously as before, was substantially doubled.

In the system of this invention, it is proposed to relate the two groups of frequencies in such a manner that the frequencies of waves transmitted from one station are intermediate those transmitted by the distant station. It has been discovered that by means of this staggered arrangement of frequencies the same desired result may be obtained as in the above-mentioned earlier arrangement as regards the total frequency interval used but with no sacrifice of clarity of tone or freedom from interference. In other words, by meansof this invention, it is possible to compress the number of frequencies transmitted in both directions within the smallest interval consistent with ellicient transmission and reception of speech signals and this is accordingly stated as one of th -objects of the invention. The desirability of using as small a frequency range as possible in carrier current signaling is shown for example, by the fact that radiation losses are greaterwvith the higher frequencies.

-l It may be stated as a further object of the invention to make possible within a' given range of frequencies, the use of a maximum number of transnnssion frequencies.

A still further object of this invention is i to enable the use of a relationship of frequencies transmitted over the line in oppo site. directions, by means of which, with a given frequency range and with a given number of frequencies, a minimum degree of interferenw results.

Proceeding to a detailed description of the invention, reference/is made to the drawing, in which the figure shows-diagramm tically the circuit connections for e plurality of transmitter and receiver circuits.

Signals may be sent over the line L to a distant station or stations irom any one or all of the "transmitter circuits T T T And the line L is adapted to transmit signals from a distant station or stations to any one or all of the receiver circuits, R R R or to any one or all oi? the alternative receiver circuits, Ill- D A The transmitter circuits T T and T are substantial duplicates; the only clili'ercncc being in the adjustn'icnts oi the various elements so that each transmitter circuit may transmit oscillations of a frequency different from that of all the others, both at the end of the line shown and at the other end of the line. The same is true of the receiver circuits R R R R R R. each of. which is tuned to the frequency or its corresponding transmitter at the other end of the line.

In each transmitter, circuit, the high treqnency osciilations produced by the oscilla- All tor O Which may be characterized as carrier oscillations are modulated in accordance with Waves by nieansof the transmittcr t and the modulator Z; The oscillator herein described is the invention of another and constitutes a part of the present invention only as one element of the system.

' The modulator-per se likewise the inyeution of another and constitutes e preferred form of means for causing the amplitude of the feeble high frequency oscillations to vary in accordance with the wave form of the message Wave; 'lhisis accomplished by impressing the message wave or impulse together with the high frequency oscillations on the input circuit of a. thermionic device 7 herein styled a modulator. The inmlulateil oscillations are amplified by the power tubes or amplifiers E2 and 3 and are impressed on the line through ,the transformer 4.

The oscillator comprises a variable transformer 8' supplied with energy from battery 9;:uariations in the battery current.

tl'irough the primary 18 causing corresponding varia ions in the F. M. induced in the secondary 11'. The frequency of the oscillations is determined by the value of the adjustable conden r 155, shunted across the adjustable primary and which forms with the latter a tuned circuit. Variations in. the lottery current are "produced by the vacuum ,lube 13 which comprises acethode ociilament i l heated by'chrrcnt supplied from battery 15 through the adjustable resistance H3. Terminal llol' the filament 14E makes an adjustable conncction'lS with the transl'orrner primal"; 10. The positive terminal 19 of l'iattury is connected to the anode or plate 20, the negative terminal 21 being con nectcd by lead 22 to one terminal of com denser 12 and one terminal of transformer primary 10, the condenser being in shunt to the primary, the other terminals of the primary and the condenser areconnected by lead to the grid 2%.

As to the operation of the oscillator, the battery 9 supplies current through a circuit including plate 20, filament. 14', lead 17, through that part of the'prin'iary 10 included by the adjustable connection 18 to the negative terminal oi the battery. This con'iprises what may be termed the sccondretry circuit of the oscillator, the prin'iary circuit of which includes filament ll, lea-d ii", that portion of transformer primary 10 between adjustable connector 18 and lead 23, and the grid Variations in the potential between filament 1% and grid Q l cause am plifiedvariations in the current delivered by the battery in the secoiulary circuit. Furthermore, the battery current in the so ondary circuit including electrode arl filament 14: is a function of the potent ial of grid 24. The two parts of the transformer primary it) are inductively related and vain the lm'l'tery current through t-lie transformer iirin'iary l0 and the period of such oscillations is determined by the adjustment of the re ulable condenser. 1% shunted across the transloriner primary l0,

Variations in th ct rrent in transformer primary .lO'cause spending variations in the M. F. induce. in the transformer secondary ii in the transmitter circuit. The oscillations set up by the transformer secondary ll arecombincd in line 25 with the oscillations produced by the transmitter t which causes variations in current supplied by battery 7) to transformer primary Qt. The line makes an adjustable connection with resistance 28 shimtcd across trans former -seoondary 27 to vary the amplitude oi? the transmitter oscillations impressed on marr l0. This productive of oscillations these-no? the grid or auxiliary electrode 29 by having its negative terminal cminectod thereto tlhe secondary circuit of modulator 5 coin ].iriscs filament 31 connected to negutive of buttery 89, the positive terminal of which is connected to the tuned ci cuit including inductaru-e 33 and capacity Lid; in parallel, thence to electrode or plate 35.

The circuit including inductance 33 and capacity 34 is tunedto the oscillator trcquency Ujld ofl' ers higl'i impedance thereto acting as an unti-resoinuit circuit, so that these high frequency iiscillutions Will be sent through condensers 36 and 3? and resistance 43. The tuned circuit 33, 3 however, offers low impedance to the passage of currents of any frequencies other than those of the oscillator frequency.

The drop in potential of the modulated high frequency oscillations across resistance l3 is impressed on the primer circuits oi the vaciuun tubes power tubes or amplifiers 2 and 3. The v muuin tube 2 encloses cathode or filament 40, anode or plate 46, and the auxiliary electrode or grid 38. Similarly the vacuum tube 3 encloses filament or cathode 41 grid 3Q, and suede or plate e27. Jondenser 36 is connected to grids 38 and 39, and condenser 37 is connected to lilainent and 411. The battery 42 has its negativetenninal connected through resist ance 43 to grids 38 and 39 While its positive terminal is connected to filaments l0 and silt The latter filaments are heated by current from battery 4st, the current being regulated by the adjustable resistance 45.

The secondary circuits of the amplifiers 2 and 3 include electrodes 6 and i? in parallel, primary 48 oi transformer i, and betterv 49 the ne utive terminal of which isconnected to the filaments l0 and l1.

T he secondary Winding 51 of transformer 4' serves as a source of amplified modulated high frequency oscillations, which are to be impressed on the line L for transmission to a properly tuned receiving apparatus at the other end of the line ln similar Way, modulated oscillations may be impressed on the line L by means of transformers 5 and 6 in the transmitter circuits T and T respectively.

The elements of the transmitter circuits T and T are identical with those of transmitter circuit T the only difference being in the adjustment of the various circuits whereby each transmitter circuit impresses on the line L a carrier frequency different from that impressed. by he other transnutter circuits. i It would be unsatisfactory to have the secondary windings of transformers 4, 5 and 6 directly connected in the line L because each secondary Windingwould serve as choirs coil for current transmitted from all ot the others end each secondary Winding would thereby impede the passage oi": the high frequency currents,

To effective y rcn'iore the impedance that secondary xvii 5i. wou d otherwise oil'er to currents from transnniter circuits other than T the anti-rsonaut circuit C is connccied in shunt to the winding 51. This auti rcsonant circuit comprises condenser 55 51nd inductance which are supplied in parallel by the whirling 5i.

'ihc ai'iti-resonant circuit 0 is tuned to the high trequcncy supplied by transmitter circuit T The auti-resoiniut circuit (l then otters a path of high impedance to currents supplied by transmitter circuit T and these curl-cuts llow to the line L through the coinparativoly low resistance path provided by the elements .31 and This low resistance path is tuned to the i'rcipienc supplied by transmitter circuit- 'l by means of adjustable (ondensc-r St).

The currents supplied by transmitter circuits T "i or by the transmitter circuits at the other end of the line, being of a froqucncy diii'erent iron) that fOPWlllCll antiresonant circuit C is "tuned, find this antiresonant circuit a path of low impedance.

is to be noied then tlnrt an unti-rcsonuut circuit, coui u'ising an inductance and a capacity supplied from a source in parallel, when tuned to the 'lrequeucy of the source, provides a high impedance path to currents from that source and a low in'ipedance path to currents of other frequencies. The usual type of oscillation circuit includes an inductance and :1 capacity connected in series with a source and tuned to the frequency of that source in order that this circuit may be more receptive to currents from that source than to currents of frequencies difierent cordingi ly here used to designate. a circuit which otters higrh impedance to the passage of currents of the frequency to which it tuned, but which provides a low impedance path for current-s oi other frequencies.

In a manner similar to that described in connection with transmitter circuit T the transmitter circuits T and T are provided with adjustable coni'lensera 52 and and with anti-resonant circuits C and re spectively. inductance 56 and capacity 57 are provided in anti-resonant circuit C and auti-resonant circuit C includes inductance 58 and condenser 59. rlrnti-rcsonantcircuits C and C are tuned to the frequencies supplied by transmitted circuits T and T respectively.

Each of the transmitter circuits T Il T supplies carrier oscillations of a nequency different from those supplied by the remaining transmittercircuits. Hence, each anti-resonant circuit provides a path of high impedance for currents from its associated.

T he loczil transmitting L, conventionally represents a plurality of receiver circuits, each of which is tuned to the frequency of one of the transmitter circuits T T T Coni ectcd in. the line L is the transformer primary (3U, adjustable with respect to the secondary {31. which supplies the energy of the incoming signals to the receiver circuits n R2: R31 u n R2,: i

To provide it balancing network for this system, transmitter lead (32. is connected to the line L While lead 63 is connected to the middle point (i l ot' primary 60. Betweenthe primary '80 and thepoint of connection of lead 69 with line L there is connected an artificial line 65 which, for the reasons fully disclosed in the above mentioned patent should preferzibly be non-reactive, i. e. consist of a substantially pure resistance.

Viewing the connections in a diil'erent way the artificial line'ti5 and that part of primary winding connected between it and the'connection 6 comprises a bridge connection, or shunt about the'transmitte'r circuits connected to leads 62 and 63, If the impedance of artificial line 65 is exactly the same as the impedance of the line L. then currents clue to transmitter circults T T T in the tivo hsl 'es of primary winding-60 will be equnl'in value, and as these currents How in opposite directions in the two halves of the primary Winding 60, the resultant effect on the secondary til is nil, so that the outgoing energy has no cfiect on the local receivingapparatus. However, current of the incoming signals passes in the same direction through the two parts of primary 60, so that the incoming energy is transferred to the locel receiving'apgtaarstusl path 62, 56, 58., 63 and the local receivingpath 7%, 76, T5, are therefore conjugate at the carrier frequencies. w I

The transformersecondary 61 is connected either to the receiver circuits R R R or to receiver circuits R R R if it is desired to separate the difi'erent firequen} 'ics betore amplifying and detecting, the transformer secondary ol is connected to receiver circuits R R R connection being; made by lines 66 and. to primary windings of the adjust-able transformers 58, 69 and 70. By n'ieans of the variable condensers 71,

'72 and 73 the secondary circuits of transi formers 68, 69 and '70 arejeuch tuned to the carrier frequency supplied by the c'orre 1 spending transmitter circuit at tnevother end, of the line L. The transmitter and receiver.

circuitsot the other end. of the line are similar to thoseshovrn mdetsil and ere convene characteristic, it tends to not use In device andif the transmitted as Well asthe v circuit comprising the Lessee-i or input circuit of the amplifier '36 which comprises the evacuated vessel 77, enclosing cathode or filament 78'heated by better *T'Q, the grid or auxiliary electrode an plate or anode 81. line 74; is connected to 'the'grid 80 and line 75 to the filament 7B. The secondary or output circuit of the am plifier 76 comprises anode 81, the primer windings of the variable transformers 83, 8 2: 85, in series, and the battery 82, the negacathode 78. it will be noted that since the amplifier '76 does not have an exact-1v linear ulating received high frequency currents were allowed to act tllfllQEPOhglt would tend to cause internioduletion hetween the trans mitted and received currents.

the

time terminal of which is connected to the 1 Amplified modulated oscillations of a given frequency are selected by the tuned secondary winding of transformer 83 and the veriable condenser 86, shunted thereacross, and these oscillations are impressed on the inputcircuit of the detector 87. This detector comprises an evacuated vessel 88 which encloses cathode 89 heated by battery 90, grid 91 and plate 92, the gridfil and filament 89 forming the terminals of the grimary or input circuit connected to the secondary Winding of transformer 83, The anode 92 and cathode 89 are the terminals of the dc tector output circuit and Which. includes the battery 93, having its negative terminal 'honnected to the cathode 89, and the priinary Winding of transformer 94:,the secondary of "which is connected to the receiver 35, 1 The receiving circuits R and R are substsntial duplicates of receiving circuit It the only difference being in the adjustments of the condensers and inductances, Where by each is tuned to at frequency different from that of the others, this frequency beingthat of the oscillations furnished by the generator in the corresponding transmitter circuit attire lit nre'terred term, the incoming Waves are other end of the line.

einplifiecl in a single deviceand then transm tted I where they .nre selected and detected to to thewsrious receiving circuits will he epnarent, therefore, that in the yield the signal currents which are supplied to the respective signal indicating instruments or receivers.

The above description of the structure and arrangements of circuits is the same as that disclosed in the patent referred to above. It is the-essence of this invention, however, that the transmitting frequencies of circuits T T and T, shall have a certain definite relation to the frequencies of the station T. For example, if it be assumed that the carrier frequencies of circuits T T T are respectively 5,000, 10,000 and 15,000 cycles, the corresponding frequencies of currents at station T may be 7,500, 12,500 and 17,500. It necessarily 01 lows that the trequencie-s to which receiving circuits R R R, are tuned are re spcctively 7,500, 12,500 and 17,500. That this staggering of frequencies can be accomplish without unduly increasing interference can be shown by the following explanation "of the phenomenon:-

The ctl'iciency of a system such as that disclosed is largely measured and determined by the presence or absence of interference. There may be interferences between the receiving circuits at a station, whereby an incoming signal from the distant station may influence a receiver other than the one tuned to the particular carrier frequency. This results in the phenomenon of crosstalk. Or signals transmitted over the line by any one of the transmitters T T T may influence receiving circuits R R this phenomenon being known as side tone. Cross-talk can be eliminated by sharply tuning the receiving circuits, the minimum frequency interval between adjacent receiving circuits, and hence between transmiting circuits, being dependent upon the (le ee of selectivity secured by the particuiar tuned circuits used and on the maximunfal- -1owable interference. Interference between the transmitting circuits is slight as compared with interference between receiving circuits. Side tone can be largely eliminated by the balancing net-work including the artificial line 65, as has been pointed" out. I

The balancing net-work therefore can be made much more effective'than the timed circuits for the purpose of eliminating side tone interference, and hence a smaller frequency difference between circuits T, and R for example, than between T and T or R, and R is allowable. It the ire quencies transmitted in the two directions for each chailnel were the same and the frequency interval between T,, T, and T, and R R and R was the minimum permissible to reduce cross-talk to a satisfactory value, the balancing network would" not be eli'ective for eliniiniating side tone. However, if the group of frequencies trans- ,ae'r

mitted from one station, that is, R 3,, it, or T,, T,, T, were displaced so that the frequency interval between them and that between the frequencies of the other group is maintained a ruinin'ium to eliminate inlcrtcrence due to crosstalk while the frequency interval between the successive trequencics used in this system is made approximately oue-halt that between the trequencies within each group, a system which would operate satisfactorily would be novided. in sucha system, the frequencies of the waves transn'ii'ttc'd in opposite direc tions will alternate with one another, while without changing the frequency} interval for reducing cross-tall: to satisfactory value, a frequency spacing that will enable the balancing network to eliminate side tone is provided.

Using the same frequency interval as before between receiving circuits, the tre quency transmitted from one station will be 5, l0 and 15 thousand, and the frequenties transmitted from the other stations will be 7,500, 12,500 and 17,500. In order not to exceed the permissible cross-tall; interference. it has been found that with the staggered arrangement described above, it is necessary to increase somewhat the frcqucncyintcrval between receiving circuits. However. in spite of this increase there results a large net gain over the arrangement heretofore used in practice, which involved completely separating the two frequency groups. Although per haps as great a frequency interval as has been indicated above between frequencies of circuits T and it, etc, is not necessary in order that interference between these circuits shall not exceed the practical limit which determined tie spacing of T T etc., it is pointed out that the overall frequency range is not substantially increased by caus- .ing the frequency interval between T, and R for example, to be as great as halt the frequency interval between T, and T, or R, and R, instead of the smallest pe missible frequency intcrva which would reduce side-tone to such a value tl at its interference would be negligible. and that with this spacing there will resulta mini mum amount of side tone interference. Accordingly, the arrangement dcsm'ibed is to be preferred,although the nvention is not necessarily so limited. Nor are the frequency values given to be considered as more than illustrative. necessary, or even desirable, that the interval between successire transmitting Freqiuincics including frequencies in both directions be the same tnroughout theirs quency range. The most cthcient spacing is that in which the frequency interval is larger as the frequency becomes greater. F or example, the following frequencies may In fact it is not.

till

he used in telephone transmission 2%, :26, 3:2, 3%, tel, 50, 55, 62, TO, 78, 86, and thousand cycles. in general it would be desirable to have the incrcasein frequency diilerences more uniform.

For carrier current telegraphy the following vulueshave been used in one dircction: 3350, 3850, i350, 4e80, 5e50,- 6090, 6790, 758 $470,9 l60; and the following frequencies in the other direction: 3600, 4100, i610, moo. 5760, we, me, 8010, 8950, 10,000. The respective frequencies differences are then, 250, 250, 250, 243i), 260, 270, 220, 290, 310, 330, 34.0, sec, see, in), 430, 4-60, 480, 510, MO. It is seen that these intervals increase progressively as the car-- ricr frequencies forming the boundary frequency. for-these intervals, respectively, increase considering either the. lower or the higher 01: the two boundary frequencies as the reference frequency throughout the range. Although the. frequency intervals vary from 250 to 5 l0 in the case stated, it is sometimes desirable to make them vary from as low a frequency 100 cycles and to a higher frequency than that given. As has been pointed out previously this frequency interval is determined by the degree of selectivity secured by the tuned circuits and by the lordancedcircuits, more particularly by the former. Experimental tests have furnished. date from which curves have been plotted, for difl'ercnt degrees of selectivity between frequencies transmitted and corresponding intervals. These curves, extended, would pass through the origin and the coordinates progressively increase or decrease together but the curves are not linear, as is indicated for example by the values given above in which the ratio of frequency diil'erence to boundary frequency decreases as the boundary frequency increases.

Although the numerical example given shove has reference to 't-clegraphy, the underlying; theory and reasoning apply equally well to any system using a plurality of carrier frequencies would apply to telephony.

It should be explcined that it is not nec 'essary for a conversation to be carried on over circuits which have adjecenttrequencies, nor is it nccessery that the two frequencies required for conversation have the same relation with each other for each pair of circuits comprising a conversational unit. There are in fact practical reasons urging the use of frequencies as widely dill'erent as possible. For example it might well happen that at a particular time the system might be used for a single conversation, (lhviously for this condition there will be the least interference when there is a maximum separation of the two frequencies corresponding to conversation. Such an urend accordingly rengcinent is not inconsistent with the use of the system to transmit the maximum number of impulses simultaneously. lhe'rc is an additional advantage in the arrangenient suggested over the simpler arrangemerit in which the adjacent frequencies are used, in that if all the circuits are simultaneously being used to transmit a plurality of conversations with the latter arrange 'ment, and ii, for any reason, the balancing network or the tuning becomes ineffective for producing suflicicnt selectivity for normal use, conversation would be IllElClQ impos sible over each of the circuits; Whereas with the form arrangement a conversation may still be carried on over any one pair of circuits and perhaps over more than one pair of circuits sufliciently separated from each other, depending on the degree of selectivity remaining.

It is to be understood that the values of frequencies given'throughout this specificationare the values of the carrier frequen cies. The frequency of the voice modu late-d wave in a carrier telephone system would vary above and below this frequency within the limits determined by the voice frequencies, the range occupied by the fre quencies corresponding to a carrier, frequency constituting a band of frequencies,

Although the drawing discloses the use' of selective tuning means at transmitting and receivin circuits for preventing intermodulation between transmitting currents and cross-talk interference between the rcceiving circuits, it is pointed out that the use oi band filters would generally be es ellective, for this purpose as the means shown, and would have certain advantages thereover in particular systems involving the invention, as forcxample in carrier tclephony, because of the comparative freedom of hand filters from distorting properties over it considerable range of frequencies. In this connection reference is made to British Patent 131,426 for a. disclosure of the use of build filters in e relation similar to that suggested.

In telephone systems it is the interference between needs rather than between the car rier frequencies that must be taken into account. Tnis Ill no Wise changes the PI'JHCF plcseboye discussed, upon which this in vention is' based, and throughout the speciiication and claims Where the carrier fre: quency is mentioned it is to be understood that bands of side frequencies may or may not he present. In general the spacing mentioned is that designed more specificall for telephony but, as is well understood: side bands may be present in telegraph or other transmission systems and t in general be comparable with the magnitude olthose in telephone systems, although probably somewhat narrower.

uese would to which essee? The adruniuges e1 the invention here stated as upplied to a carrier telephone tem apply also to other cu 'rier current signaling or other carrier current transmission systems.

The invention its bros-fleet aspect is obviously not restricted to ii: wire system. and that the line L ins-1y he incluctively or concluctively clisgioscol with reference to receiving or transmitting apparatus,

"What is claimed is:

1. A multiplex transmission system comprising a combined transmitting and receiving station, s plurality of selective trans initting circuits at seicl station, curl: a plurality of selective receiving circuits at said Staten, one of said rensinitting circuits and one of said receiving circuits being used to constitute the terminal apparatus for each two-Way unit of the system, the said truns mitting circuits being adjusted. to transmit currents of frequencies which are different from and alternating with the frequencies said receiving circuits are alljusted.

2. A multiplex transmitting system comprising a combined; transmitting and receiving station, u plurality oi? selective trans uiitting circuits at said station, means for impressing upon each oi? suicl transi'nitting circuits i high frequency current, a plureh ity of receiving circuits at said station, each selective -to the frequency of a received cur-- rent and means associated with each of said receiving circuits for oljtsining a low ire-- quency current from suicl received high fre quency current, the said transmitting circuits being adjusted to transmit currents oi frequencies which are different from and alternating with the frequencies to which said receiving circuits are adjusted: I

' A multiplex high frequency signaling system comprising a combined transmitting and receiving station." a plurality of selectire transmitting circuits. at ssicl ste lion, and u; plurality of selective receiving circuits at ssicl station, one of seicl transmitting circuits and one of serial. receiving circuits being used to co'nstiiute the terminscl appuretus"for esch two-Way unit of tlie system, the said transmitting circuits being adjustcrl to transmit currents of frcquenc'es which are (liilerent from and alternating with the frequencies to which ihc suirl receiving circuits ere adjusted.

i. A null'riples telephone system (one prising u cou'ibinccl transmitting; and receiving station, a plurality of selective trans slitting circuits at said station, means for impressing; upon each of the swirl transmitting circuits a voice inodulstedhigh fro quency carrier current, plurality of selec- -tive receivingcircuits at said stationgjunll means sssocisteci with each of receiw ing circuits for obtaining s voicecnrrent from the received high frequency current, the suirl transmitting circuits being adjust cal to transmit currents of frequencies which are different from uml alternating with the frequencies to which said receiving circuits are adjusted.

5 A multiplex transmitting system comprising a combined transmitting rind receivingstation, :1 plurality of selective transmitting circuits at said station means for impressing upon such of the Sillll iii-unsuniting circuits .a high frequency current, a plurality of selective receiving circuits at Fuirl station having a common amplifying nicuns associated therewith on the input side, and means associated .with. ccclr of said receiving circuits for obtaining u low i'requencv current from the received high frequency current, the said transmitting cir-:

cuits being adjusted to transmit currents of frequencies Which are dilierenh from and alternating with the frequencies to which said receiving circuits are adjusted.

6. A high frequency line, an incoming line and en outgoing line, conjugately conncctecl to said high frequency line, a plurality of transmitting circuits adapted for multiples carrier current transmission assorGCi with said outgoing line, and s pluru ity of receiving circuits similarly adaptiezl for multiples carrier current reception sssociutecl with said incoming line, the sairl f transmitting circuits being adjusted to.

transmit currents of frequencies which are clifl'erent fromuncl alternating with the frequencies to which said receiving circuits are udjustech 7. A transmission line, an incoming and an outgoing; circuit, means interconnectlug said line and said circuits whereby said circuits are conjugate for all frequencies tran mitted over said line, :1 plurality of modulated carrier current transmitting and detecting; circuits associated respectively with raid incoming and outgoing circuits and such selective of u liti'erc-nt currier frequency the carrier freiniencics of the said trunsinitiii-ig circuits being different from and alternating with the carrier frequencies to which said detecting circuits are adjusted.

8. A inultipicx transmitting system co1nprising a combined truusu'iitting and rece "ring station, a plurality oiselective transmitting; circuits at suirl station, means for impressing u'pon. cuch of said transmitting circuits :1 high frequency current, a plurul v of selective rcccirinncircuits at suiil station and menus ussociutecl With'each of said receiving; circuits for obtaining a low firequency cur ent from the received high frequency current, the said trunsmittin z circuits, being; adjusted to transmit currents or frequencies which are intermediate the irequencies to which shill receiving circuits are ucljiisterl, the 'l'requcncy of the current in Bil Elli-a 1 Gib lllU" (ill frequency current, the said transmitting circuits, being adjusted to transmit currents of frequencies which are different from and alternating with the frequencies to which said receiving circuits are adjusted, the frequency interval between the adjacent frequencies including those used for transmitting in both directions being'dill'erent for dill'erent parts of the frequency scaleand increasing progressively as the frequency increases 10. A s stcm es defined in claim 2, in which the transmitting and receiving cir' cuits are adg'usted to frequencies such that the intervals between adjacent carrier frequencies increase progressively over the.

range of carrier frequencies.

11. A multiples transmission system comprising two intercommunicating stations, a pluralr'y of means at each of said stations for trsnsmittingto the other station a plurality of alternating'currents, the frequen cies of the currents t-ransi'nitted by onestation being dilierent from those transmitted by the other station and alternating there with.

12. A multiplex carrier current telephone system comprising two intercommuniceting stations, a plurality of means stench of said stations for transmitting to the other station plurality or voice modulated carrier currents, the carrier frequencies oi the currents transmitted. by one station being different from those transmitted by the other station and alternating therewith.

13. n'iultiplex signaling system C0111 prising in cmnhinatiou a plurality ofcommunicating selective transmitting and receiving circuits.,, the suid transmitting cir cuits being ad'usl ed to transmit currents of frequencies which are diilercnt from and alternating with the frequencies to which said receiving circuits are adjusted.

it. A multiplex signaling system cou1- prising in combination u l'iigh frequency line, a plurality of transmitting circuits operativcly as ociated with said line, and a ydurality or receiving circuits operatively associated with mid line and adapted to cmninunicate with said transmitting cults, the said transmitting circuits heir serene"? adjusted to transmit currents of frequencieswhich ere different from and alternating vith the frequencies to which said recarving circuits are adjusted.

15. in a multiplex signaling system, a. plurality of signal channels employing dilferent frequencies divided into individual pairs each of which constitutes a two-way con versationul unit. the two channelsof each unit having adjacent frequencies and the frequencies of all the channels being so chosen that those used for transmission in one direction alternate with those used for transmission in the opposite direction.

16. A multipleir transmission system comprising two inter-commonicating stations, a plurality of means at each of said stations for transmitting to the other station a phi relity of .alteri'mting currents representing a corresponding plurality of messages, the frequencies of the currents transn'ulted by one station being diil'ercnt from those trunsmitted by the other station and ndividually alternating therewith.

17. A multiplex carrier current telephone system comprising two intercomniunicatingstations, a plurality of means at each of said stations for transmitting to'the other stetion a plurality of voice modulated carrier currents, the carrier frequencies 01'. the currents transmitted by one station being difierent from those transmittmfl by the other station and individually alternating there with. s

18.A multiplex signaling system c01nprising in combination s plurality of communieuting selective transfi'iitting circuits and a plurality of selective receiving circuits, one of said transmission circuits being used with one of said receiving circuits to constitute the terminal apparatus for each two-Way unit of the system the said trans mitting circuits being adjusted to transmit currents oi frequencies which are different from and individually alternate with the frequencies to which said receiving circuits are adjusted.

19. In a multiplex signaling system, at

plurality of signaling channels employing dill'ercnt frequencies divided into individual pairs, each of which constitutes o. two way unit, the two channels of each unit having adjacent frequencies and the frequencies of all the channels being so chosen that those used for transmission in one direction indi viduinlly alternate with those used for transu1ission,.-in the opposite direction.

20. A multiple): transmission system including s conductor for :arryiug waves corresponding to a plurality of two-Way channels. conjugately related input and out put circuits corresponding to each channel. at a terminal of said conductor, the he queue-lea transmitted in one direction alter noting with'those transmitted in the other.

. meme? 21. A multiplex transmission system employing a plurality of waves of different frequencies for transmitting in each direction, the frequencies transmitted in one direction alternating with those transmitted in the other direction, the spacing between the frequencies being increased as the higher portion of the empi oyed part of the quency range is approached.

In witness whereof, I hereunto subscribe 10 my name this 24th day of March, A. 11,:

fre-

RAYMOND A. HEISING. 

